Plunger pump device

ABSTRACT

A plunger pump device includes a housing defining a compression chamber, a plunger slidably accommodated in the housing and exposed to the compression chamber at one end, a drive cam for reciprocating the plunger, a discharge valve connected to the compression chamber, an intake valve connected to the compression chamber, and a low-pressure reservoir for accommodating fluid with a predetermined pressure or more connected to the compression chamber through the intake valve. Even if the intake valve is in a closed position, a small amount of the fluid is discharged from the compression chamber into the low-pressure reservoir side through a slit formed on the intake valve. The small amount of the fluid discharged through the slit is accommodated in a capacity space under a small pressure.

[0001] This application is based on and claims priority under 35 U.S.C. §119 with respect to Japanese Application No.2001-217536 filed on Jul. 18, 2001, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention generally relates to a plunger pump device. More! particularly, the present invention pertains to a plunger pump device suitable for such as a brake hydraulic pressure control device for a vehicle.

BACKGROUND OF THE INVENTION

[0003] Recent vehicles are provided with devices for conducting various controls such as an anti-skid control, a traction control, and a longitudinal braking force distribution control. A hydraulic pressure control device used for such controls includes a plunger pump. For example, Japanese Patent Laid-Open Publication No. H08-40234 discloses the plunger pump provided for a hydraulic pressure brake device for a vehicle. In connection with an evacuation method disclosed in the publication, in which air is evacuated from a master cylinder reservoir before brake fluid is supplied to the hydraulic pressure brake device for the vehicle, a slit is formed on a seat portion of a discharge valve for evacuation as a means for solving an issue that the brake fluid cannot be filled in a pump chamber (compression chamber) of the plunger pump. The slit for evacuation can also be formed on the seat portion of an intake valve according to the publication.

[0004] In such known plunger pump disclosed in the above publication, a noise is produced especially in a discharge mode of the pump and is required to be reduced accordingly. FIGS. 28-30 show an operation condition of known plunger pump for explaining a situation how the noise is produced. The pump includes one-way valves for an intake (intake valve) IV and for a discharge (discharge valve) OV. These valves are generally provided with a ball type valve portion and a spring for biasing the ball type valve portion. A plunger PR is reciprocated by a drive device including a drive cam DR driven by an electric motor (not shown). The volume of a compression chamber CP is reduced or expanded accordingly. The discharge side of the pump is connected to a damper chamber DP and the intake side of the pump is connected to a normally closed electromagnetic valve NC, which configures such as an actuator in the hydraulic pressure brake device disclosed in the above publication, and a low-pressure reservoir RS. As being explained later, the noise is produced especially when the intake side of the pump is in a closed space. In FIGS. 28-30, therefore, the electromagnetic valve NC, is in a closed position and the low-pressure reservoir RS is under an empty condition as being without any fluid (brake fluid).

[0005]FIG. 28 shows a final discharge mode of the pump (top dead center of the plunger PR) in which the intake valve IV is in the closed position and the volume of the compression chamber CP is reduced to a minimum volume Q. The discharge valve OV is in an open position and a gap is formed between the ball type valve portion and the seat portion. Thus, the brake fluid is discharged from the compression chamber CP into the damper chamber DP through the gap formed at the discharge valve OV. When the mode is changed from the top dead center to the bottom deed center of the plunger PR by the drive cam DR being rotated as shown by an arrow in FIG. 28, the volume of the compression chamber CP is expanded with the intake vale IV being still in the closed position. If the discharge valve OV is immediately closed at this stage, only the pressure in the compression chamber CP is decreased with the minimum volume Q of the brake fluid in the compression chamber CP. However, it takes time for the ball type valve portion of the discharge valve OV to be seated on the seat portion so that a volume ΔQ1 of the brake fluid flows from the damper chamber DP into the compression chamber CP. Thus, the brake fluid in the compression chamber CP of FIG. 29 is increased to a volume Q+ΔQ1.

[0006] When the drive cam DR is further rotated as shown by the arrow in FIG. 29 from the condition shown in FIG. 29, the drive cam DR proceeds to the top dead center of the plunger PR as shown in FIG. 30. Under this condition, the brake fluid in the compression chamber CP (Q+ΔQ1) is compressed. At this time, since the discharge valve OV is in the closed position, the pressure in the compression chamber CP is increased up to which slightly exceeds a pressure Pd in the damper chamber DP as shown by a double-dashed line at (c) point in FIG. 31. The increased pressure is transmitted to the drive cam DR through the plunger PR, which results in a cause of the noise at the motor portion (not shown). (a) and (b) points in FIG. 31 show the pressure in the compression chamber CP under the conditions of FIGS. 28 and 29 respectively.

[0007] In this case, if the slit is formed on the seat portion of the intake valve for evacuation as being adopted in the pump disclosed in the above publication, a volume ΔQ2 (approximately equal to ΔQ1) of the brake fluid is discharged from the compression chamber CP through the slit. However, the intake side of the pump is a closed hydraulic pressure passage as mentioned above, the pressure in the compression chamber CP is increased until it becomes approximately equal to the pressure in the damper chamber DP. As shown in FIG. 28, a resin seal member SL is provided at the plunger PR. Since this seal member SL does not function as a perfect seal, a small gap is provided thereat. However, in the same manner as the above slit, the intake side of the pump is the closed hydraulic pressure passage so the pressure in the compression chamber CP cannot be decreased. In addition, since the gap is formed unequally or irregularly, the seal member SL cannot be used as a communication hole for measures against the incidence of the noise without any specific arrangements.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide a plunger pump device with a simple structure which can decrease a noise caused by an operation of a discharge valve. It is another object of the present invention to provide a plunger pump device in which an intake side is connected to a low-pressure reservoir. It is a further object of the present invention to provide a plunger pump device being applied not only for a hydraulic pressure brake device for a vehicle but also for a wide range of hydraulic devices.

[0009] According to an aspect of the present invention, the plunger pump includes a housing defining a compression chamber, a plunger slidably accommodated in the housing and exposed to the compression chamber at one end, a drive means for reciprocating the plunger, a discharge valve connected to the compression chamber, an intake vale connected to the compression chamber, and a low-pressure reservoir for accommodating fluid with a predetermined pressure or more connected to the compression chamber through the intake vale. The plunger pump also includes a discharge permitting means for permitting a small amount of the fluid to be discharged from the compression chamber into the low-pressure reservoir side even if the intake valve is in a closed position, and a capacity means having a capacity space for accommodating the small amount of the fluid discharged from the discharge permitting means and for accommodating the fluid under a small pressure less than the predetermined pressure.

[0010] In the above-mentioned plunger pump, the intake valve is provided with a valve seat and a valve portion always biased to be seated on the valve seat. A slit is formed on at least either one of the valve portion or the valve seat for preferably configuring the discharge permitting means. Due to this discharge permitting means, the small amount of the fluid is discharged from the compression chamber to the low-pressure reservoir side even if the intake valve is in the closed position.

[0011] The plunger can be slidably accommodated in the housing through a seal member for permitting the small amount of the fluid to be discharged from the compression chamber. The discharge permitting means can be configured by the seal member.

[0012] The low-pressure reservoir is preferably provided with a cylinder connected to the compression chamber through the intake valve, a piston slidably accommodated in the cylinder and forming a fluid chamber for accommodating the fluid in the cylinder, and a biasing means for biasing the piston in a direction in which the volume of the fluid chamber is reduced.

[0013] The piston in the present invention is formed with a concave portion being covered by a diaphragm member on a surface of the piston exposed to the fluid chamber. The capacity space of the capacity means is preferably configured by an expanded space formed in the fluid chamber when the diaphragm member is deformed inside the concave portion. The diaphragm member can be integrally formed with the piston.

[0014] An annular groove can be formed on an outer periphery of the piston and an annular elastic member can be inserted into the annular groove for forming a predetermined space therebetween in a sliding direction of the piston. The capacity space of the capacity means can be configured by an expanded space formed between the annular elastic member and the annular groove when the annular elastic member is deformed.

[0015] A reverse biasing means is provided for biasing the piston in a reverse direction to a biasing force of the above biasing means. The capacity space of the capacity means is configured by an expanded space in the fluid chamber being expanded by adjusting the biasing force of the reverse biasing means relative to that of the biasing means. The reverse biasing means in the present invention is preferably an elastic member disposed between the piston and the cylinder. For the elastic member, such as a coned disc spring, a coil spring, and an elastic resin ring are available.

[0016] The capacity means can be provided with a sub-cylinder formed at the piston for communicating to the fluid chamber, a sub-piston slidably accommodated in the sub-cylinder and forming a sub-fluid chamber for accommodating the fluid in the sub-cylinder, and a sub-biasing means for biasing the sub-piston in a direction in which the volume of the sub-fluid chamber is reduced.

[0017] The capacity means can be provided with the sub-cylinder formed at the housing for communicating to the fluid chamber, the sub-piston slidably accommodated in the sub-cylinder and forming the sub-fluid chamber for accommodating the fluid in the sub-cylinder, and the sub-biasing means for biasing the sub-piston in the direction in which the volume of the sub-fluid chamber is reduced.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0018] The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures in which like reference numerals designate like elements and wherein:

[0019]FIG. 1 is a cross sectional view of a plunger pump device according to a first embodiment of the present invention;

[0020]FIG. 2 is a cross sectional view of the plunger pump device according to a second embodiment of the present invention;

[0021]FIG. 3 is an enlarged cross sectional view of a part of the plunger pump device according to the another embodiment of the present invention;

[0022]FIG. 4 is a cross sectional view of a first embodiment of a low-pressure reservoir used in the present invention;

[0023]FIG. 5 is a cross sectional view showing a part of an operation condition of the first embodiment of the low-pressure reservoir;

[0024]FIG. 6 is a cross sectional view of a second embodiment of the low-pressure reservoir used in the present invention;

[0025]FIG. 7 is a cross sectional view showing a part of an operation condition of the second embodiment of the low-pressure reservoir;

[0026]FIG. 8 is a cross sectional view of a third embodiment of the low-pressure reservoir used in the present invention;

[0027]FIG. 9 is a cross sectional view showing a part of an operation condition of the third embodiment of the low-pressure reservoir;

[0028]FIG. 10 is a partially enlarged sectional view of FIG. 9;

[0029]FIG. 11 is a cross sectional view of a fourth embodiment of the low-pressure reservoir used in the present invention;

[0030]FIG. 12 is a cross sectional view showing a part of an operation condition of the fourth embodiment of the low-pressure reservoir;

[0031]FIG. 13 is a partially enlarged sectional view of FIG. 12;

[0032]FIG. 14 is a cross sectional view of a fifth embodiment of the low-pressure reservoir used in the present invention;

[0033]FIG. 15 is a cross sectional view showing a part of an operation condition of the fifth embodiment of the low-pressure reservoir;

[0034]FIG. 16 is a cross sectional view of a sixth embodiment of the low-pressure reservoir, used in the present invention;

[0035]FIG. 17 is a cross sectional view showing a part of an operation condition of the sixth embodiment of the low-pressure reservoir;

[0036]FIG. 18 is a cross sectional view of a seventh embodiment of the low-pressure reservoir used in the present invention;

[0037]FIG. 19 is a cross sectional view showing a part of an operation condition of the seventh embodiment of the low-pressure reservoir;

[0038]FIG. 20 is a cross sectional view of an eighth embodiment of the low-pressure reservoir used in the present invention;

[0039]FIG. 21 is a cross sectional view showing a part of an operation condition of the eighth embodiment of the low-pressure reservoir;

[0040]FIG. 22 is a cross sectional view of a ninth embodiment of the low-pressure reservoir used in the present invention;

[0041]FIG. 23 is a cross sectional view showing a part of an operation condition of the ninth embodiment of the low-pressure reservoir;

[0042]FIG. 24 is a cross sectional view of a tenth embodiment of the low-pressure reservoir used in the present invention;

[0043]FIG. 25 is a cross sectional view showing a part of an operation condition of the tenth embodiment of the low-pressure reservoir;

[0044]FIG. 26 is a graph showing a relationship between a pressure in a fluid chamber of the low-pressure reservoir and a stroke of a piston according to some embodiments of the low-pressure reservoir used in the present invention;

[0045]FIG. 27 is a graph showing a relationship between the pressure in the fluid chamber of the low-pressure reservoir and the stroke of the piston according to remaining embodiments of the low-pressure reservoir used in the present invention;

[0046]FIG. 28 is an explanatory view of an operation condition of a known plunger pump, and especially showing a condition when a plunger is in a top dead center;

[0047]FIG. 29 is an explanatory view of an operation condition of the known plunger pump, and especially showing the condition when the plunger is moved from the top dead center to a bottom dead center;

[0048]FIG. 30 is an explanatory view of an operation condition of the known plunger pump, and especially showing the condition when the plunger is moved to a next top dead center;

[0049]FIG. 31 is a graph illustrating a pressure condition in a compression chamber corresponding to the plunger position according to the general plunger pump and the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0050] Referring now to embodiments of the present invention with reference to the attached drawings, FIG. 1 shows a first embodiment of a plunger pump of this invention. A damper chamber DP and a compression chamber CP are defined in a housing 1 in which holes 1 a and 1 b connected to the compression chamber CP are formed. A plunger 2 is slidably accommodated in the hole 1 a being exposed to the compression chamber CP at one end.

[0051] The plunger 2 of the present embodiment has a spool shape and includes an annular groove 21 at a center into which a seal member S1 is disposed. The plunger 2 is slidably moved within the hole 1 a under the condition that a front and a back of the seal portion S1 are hydraulically sealed. As a drive means for driving the plunger 2 to reciprocate, a drive cam 4, which is rotated by an electric motor (not shown) with reference to a shaft 3 being orthogonalized with an axis of the hole 1 a, is provided. By a coil spring 5 disposed between a seat member 6 a being mentioned later and the plunger 2, the plunger 2 is biased to press and be in contact with a peripheral cam surface of the drive cam 4. An end side of the plunger 2 in contact with the drive cam 4 is at atmospheric pressure. Accordingly, since the drive cam 4 is rotated with reference to the shaft 3 located in an eccentric position to the center of the drive cam 4, the plunger 2 being in contact with the peripheral cam surface is reciprocated in the hole 1 a. In this embodiment of the present invention, the plunger 2 is reciprocated one time per one rotation of the drive cam 4.

[0052] The compression chamber CP is connected to a discharge valve 6 and an intake valve 7 through the hole 1 b. The discharge valve 6 of this embodiment configuring a one-way valve is provided with the seat member 6 a being fitted to the compression chamber CP, a ball type valve portion 6 b to be seated on a valve seat provided around a discharge hole 6 e formed at the seat member 6 a, a coil spring 6 c biasing the ball type valve portion 6 b in a direction to be seated, and a retainer 6 d engaged with the seat member 6 a for holding the coil spring 6 c. In the same way, the intake valve 7 of this embodiment configuring the one-way valve is provided with a seat member 7 a being fitted to the hole 1 b connected to the compression chamber CP, a ball type valve portion 7 b to be seated on the valve seat provided around an intake hole 7 e formed at the seat member 7 a, a coil spring 7 c biasing the ball type valve portion 7 b in the direction to be seated, and a retainer 7 d engaged with the seat member 7 a for holding the coil spring 7 c.

[0053] On the valve seat around the intake hole 7 e where the ball type valve portion 7 b is seated, a small slit 7 s is formed. Therefore, even if the intake valve 7 is in a closed position as the ball type valve portion 7 b is seated on the valve seat around the intake hole 7 e, a small amount of fluid is discharged from the compression chamber CP into a side of a low-pressure reservoir 10. Thus, a discharge permitting means of the present invention is configured by the slit 7 s according to the first embodiment.

[0054] The low-pressure reservoir 10 is connected to the aforementioned intake valve 7 and thus connected to the compression chamber CP through the intake valve 7. The low-pressure reservoir 10 of this embodiment is configured in a same manner as those of FIGS. 4, 5 and can accommodate the fluid with a predetermined pressure or more. That is to say, a piston 11 is slidably accommodated in a cylinder 10 a connected to the compression chamber CP through at least the intake valve 7. A fluid chamber CF is formed between a top surface of the piston 11 and an inner wall of the cylinder 10 a. The fluid chamber CF and the cylinder 10 a provided on the other side with reference to the piston 11 is hydraulically separated through a seal member S2, which is provided on an outer periphery of the piston 11. A coil spring 12 is disposed as a biasing means for biasing the piston 11 in a direction in which the volume of the fluid chamber CF is reduced. Thus, the fluid with the predetermined pressure or more overcoming the biasing force of the coil spring 12 is accommodated in the fluid chamber CF. A plate 13 including a hole 13 a at the center is a member for supporting the coil spring 12. A side of the coil spring 12 of the plate 13 within the cylinder 10 a is connected to air through the hole 13 a.

[0055] In the low-pressure reservoir 10 of this embodiment, a stepped concave portion comprised of concave portions 11 a and 11 b is formed on the top surface of the piston 11 being exposed to the fluid chamber CF. At the stepped portion, a diaphragm member 14 is provided so as to cover the concave portion 11 b and is secured by an annular member 15. A bottom surface of the concave portion 11 b is formed with a communication hole 11 c. Accordingly, a space is formed between the diaphragm member 14 and the concave portion 11 b. A capacity space of this invention is configured by an expanded space formed by the diaphragm member 14 being deformed inside the concave portion 11 b. At this time, since the space between the diaphragm member 14 and the concave portion 11 b is connected to air through the communication hole 11 c, the diaphragm member 14 is deformed inside the concave portion 11 b by the fluid flowing into the fluid chamber CF with a small pressure less than the predetermined pressure. Thus, in the expanded space formed on the top surface of the diaphragm member 14, the fluid is accommodated under the small pressure.

[0056] The operation of the plunger pump device of the present embodiment will be explained as follows. The plunger 2 is reciprocated within the hole 1 a by the drive cam 4 being rotated with reference to the shaft 3. The plunger 2 is moved rightward of FIG. 1 and then the volume of the compression chamber CP is expanded. When the intake valve is opened (the discharge valve 6 is closed), the fluid (for example, brake fluid) is supplied from the fluid chamber CF of the low-pressure reservoir 10 to the compression chamber CP through the intake hole 7 e of the intake valve 7. When the plunger 2 is moved leftward of FIG. 1, the volume of the compression chamber CP is reduced, and the intake valve 7 is closed. At the same time, the discharge valve 6 is opened and the fluid in the compression chamber CP flows out to the damper chamber DP.

[0057] In the above operation, when the plunger 2 is moved from the top dead center thereof (left end position) to rightward, a small amount of the fluid (brake fluid) flows into the compression chamber CP until the ball type valve portion 6 b of the discharge valve 6 is seated on the seat member 6 a. This excessive fluid flows into the side of the lowpressure reservoir 10 through the slit 7 s formed on the intake valve 7 even if the intake valve 7 is in the closed position. The fluid discharged through the slit 7 s flows into the fluid chamber CF of the low-pressure reservoir 10 and accommodated in the expanded space formed on the top surface of the diaphragm member 14 being deformed inside the concave portion 11 b. Accordingly, the pressure in the compression chamber CP is not excessively increased as shown by a solid line in FIG. 31 and the incidence of the noise by the plunger 2 can be prevented.

[0058]FIG. 2 shows the second embodiment of the plunger pump device. Instead of the plunger 2 and the intake valve 7 in FIG. 1, a plunger 20 and an intake valve 70 are employed. The low-pressure reservoir 10 is connected to the compression chamber CP through the plunger 20 and the intake valve 70. In the second embodiment, a hole 1 c connecting the compression chamber CP and the damper chamber DP is provided. A discharge valve 60 is fitted to the hole 1 c. The compression chamber CP is defined by a plug member 8 being secured to the housing 1 and the intake valve 70 is accommodated in the compression chamber CP.

[0059] As shown in FIG. 2, the plunger 20 of the second embodiment is formed with an annular groove 21, a hole 22 in the axial direction opening in the compression chamber CP, a communication hole 23 connecting the annular groove 21 and the hole 22. An annular seal member S3 is provided on the side of the compression chamber CP and an annular seal member S4 is provided on the side of the drive cam 4 relative to the annular groove 21. A fluid chamber CG formed by the annular groove 21 and the, housing 1 is connected to the fluid chamber CF (not shown in FIG. 2) of the low-pressure reservoir 10 as shown by a dashed line in FIG. 2. The seal member S4 on the side of the drive cam 4 functions as a perfect seal as being made of rubber, however, the seal member S3 on the side of the compression chamber CP does not function as the perfect seal as being made of resin. Thus, a small amount of the fluid is discharged from the compression chamber CP through the seal member S3. As shown in more detail in FIG. 3, the upper drawing shows an initial position condition of the seal member S3. In FIG. 3, the resin seal member S3 is inserted into the annular groove 24 of the plunger 20 so as to form a small space therebetween. The lower drawing in FIG. 3 shows a compressed condition of the seal member S3 under which a hydraulic passage is formed between the annular groove 24 and the seal member S3 for permitting the small amount of the fluid to flow from the compression chamber CP. Accordingly, the discharge permitting means of the present invention is configured by the seal member S3 according to the second embodiment.

[0060] As the configuration of the low-pressure reservoir connected to the compression chamber CP through the intake valve 7 or the intake valve 70 and the plunger 20 as shown in FIGS. 1, 2, not only the low-pressure reservoir 10 shown in FIG. 1 but also various kinds of the low-pressure reservoir being explained as follows can be used. FIGS. 4, 5 show the low-pressure reservoir of the first embodiment used in this invention. The low-pressure reservoirs in FIGS. 4, 5 are same as that in FIG. 1, so an explanation thereof is not repeated here. FIG. 4 shows the condition before the low-pressure reservoir is operated as the capacity means and FIG. 5 shows the condition when the low-pressure reservoir is operated as the capacity means. When the fluid flows into the fluid chamber CF, the diaphragm member 14 is deformed inside the concave portion 11 b. The fluid is accommodated in the expanded space formed on the diaphragm member 14 as shown in FIG. 5. The capacity space in the present invention is configured by the expanded space formed in such a manner.

[0061] The fluid in the expanded space formed on the concave portion 11 b in the diaphragm member 14 is received under the small pressure due to an elastic deformation of the diaphragm member 14. The relation between the stroke of the piston 11 and the pressure in the fluid chamber CF of the low-reservoir 10 is shown by a solid line in FIG. 26 indicating that the stroke of the piston 11 cannot be obtained until the pressure of the low-pressure reservoir becomes a predetermined pressure (Pb) or more. However, in the first embodiment of the low-pressure reservoir, as shown by a dashed line in FIG. 26, the small stroke (Da) of the piston 11 is obtained by a small pressure (Pa) less than the predetermined pressure (Pb). The fluid with the small pressure (Pa) is accommodated due to the effect of the capacity means (diaphragm member 14 and concave portion 11 b) on the pressure in the fluid chamber CF. When the pressure on the side of the fluid chamber CF is decreased, the fluid in the expanded space on, the concave portion 11 b in the diaphragm member 14 is returned to the fluid chamber CF by the elastic force of the diaphragm member 14.

[0062]FIGS. 6,7 show the second embodiment of the low-pressure reservoir used in the present invention. FIG. 6 shows the condition before the low-pressure reservoir is operated as the capacity means and FIG. 7 shows the condition when the low-pressure reservoir is operated as the capacity means. In the second embodiment, the diaphragm member; 14 is integrally formed with the piston 11. For example, when the piston 11 is molded from resin, the diaphragm member 14 of the elastic resin material is integrally molded with the piston 11. Thus, the annular member 15 of the first embodiment in FIGS. 4, 5 is not required so the number of parts and the production process are reduced. Since the 4 rest configuration of the second embodiment of the low-pressure reservoir used in the present invention is substantially same as that of the embodiment in FIGS. 4, 5, the substantially same parts or components shown in FIGS. 4, 5 bear the same numbers in the second embodiment.

[0063]FIGS. 8, 9 show the third embodiment of the low-pressure reservoir used in the present invention. FIG. 8 shows the condition before the low-pressure reservoir,is operated as the capacity means and FIG. 9 shows the condition when the low-pressure reservoir is operated as the capacity means. FIG. 10 is an enlarged view of a part of FIG. 9 in which hatching of a seal member S5 is omitted for easy understanding. In the third embodiment, the seal member S5 being inserted into an annular groove 16 formed on the outer periphery of the piston 11 is formed in a different shape from the seal member S2 of the above first embodiment. A predetermined space is formed between the seal member S5 and the annular groove 16. The seal member S5 configuring the annular elastic member of the present invention has an approximately X-shaped section and is configured to form the predetermined space between the annular groove 16 having an approximately rectangular section when inserted thereto. Since the rest configuration of the third embodiment of the low-pressure reservoir used in the present invention is substantially same as that of the embodiment in FIGS. 4, 5, the substantially same parts or components shown in FIGS. 4, 5 bear the same numbers in the third embodiment and the explanation is not repeated here.

[0064] As shown in FIG. 9, when the fluid flows into the fluid chamber CF, the seal member S5 is pressed to one side of the annular groove 16 (lower side of FIG. 9) by the small 4 pressure of the fluid. At the same time, a portion of the seal member S5 in contact with the annular groove 16 is deformed so as to be tightly contacted with an inner surface of the annular groove 16. Accordingly, an expanded space CL is formed as shown in FIG. 10 and the capacity space of this invention is configured thereby. The fluid flows into the space formed within the annular groove 16 including the expanded space CL and is accommodated under the small pressure due to the elastic deformation of the seal member S5. That is to say, as shown by the dashed line in FIG. 26, the small stroke (Da) of the piston 11 is obtained by the small pressure (Pa) less than the predetermined pressure (Pb). The fluid with the small pressure (Pa) is accommodated due to the effect of the capacity means (seal member S5 and annular groove 16) on the pressure in the fluid chamber CF. When the pressure on the side of the fluid chamber CF is decreased, the fluid in the expanded space CL is returned to the fluid chamber CF by the elastic force of the seal member S5. In the third embodiment of the low-pressure reservoir used in the present invention, since the configuration thereof is same as that of the first and second embodiments of low-pressure reservoir and only the seal member S5 is required to be provided, production is simple.

[0065]FIGS. 11,12 show the fourth embodiment of the low-pressure reservoir used in the present invention. FIG. 11 shows the condition before the low-pressure reservoir is operated as the capacity means and FIG. 12 shows the condition when the low-pressure reservoir is operated as the capacity means. FIG. 13 is an enlarged view of a part of FIG. 12 in which the hatching of a seal member S6 is omitted for easy understanding. In the fourth embodiment, the capacity space of the present invention is configured by the expanded space (shown as CL in FIG. 13) formed between the seal member S6 and the annular groove 16 in the same manner as the embodiment in FIGS. 8, 9. However, the expanded space CL is formed in a different shape from the seal member S5 of the embodiment in FIG. 8, 9. The seal member S6 configuring the annular elastic member of this invention has an approximately U-shaped section and is configured to form a predetermined space between the annular grodve 16 having the approximately rectangular section when inserted thereto.

[0066] As shown in FIG. 12, when the fluid flows into the fluid chamber CF, the seal member S6 is pressed to one side of the annular groove 16 (lower side of FIG. 12) by the small pressure of the fluid. At the same time, a portion of the seal member 56 in contact with the annular groove 16 is deformed so as to be tightly contacted with the inner surface of the annular groove 16. The fluid in the annular groove 16 including the expanded space CL being formed by the above-mentioned manner is accommodated under the small pressure due to the elastic deformation of the seal member S6. As shown by the dashed line in FIG. 26, the small stroke (Da) of the piston 11 is obtained by the small pressure (Pa) and the fluid with the small pressure (Pa) is accommodated. Since the rest configuration of the fourth embodiment of the low-pressure reservoir used in the present invention is substantially same as that of the embodiment in FIGS. 8, 9, the substantially same parts or components shown in FIGS. 8, 9 bear the same numbers in the third embodiment and the explanation is not repeated here. Also in the fourth embodiment, only the seal member S6 is required to be provided, the production is simple.

[0067]FIGS. 14, 15 show the fifth embodiment of the low-pressure reservoir used in the present invention. FIG. 14 shows the condition before the low-pressure reservoir is operated as the capacity means and FIG. 15 shows the condition when the low-pressure reservoir is operated as the capacity means. In the fifth embodiment an elastic member is disposed as a reverse biasing means between the piston 11 and the cylinder 10 a for biasing the piston 11 in a reverse direction to a biasing direction of the coil spring 12. Further, in the fifth embodiment, a coned disc spring 17 is used as the elastic member. The capacity space of the present invention is configured by an expanded space formed when the volume of the fluid chamber CF is expanded by adjusting the biasing force of the coned disc spring 17 relative to that of the coil spring 12.

[0068] In an inoperative condition of the capacity means as shown in FIG. 14, a clearance formed between the inner surface of the piston 11 and that of the cylinder 10 a is adjusted to be D1 due to the biasing force of the conned disc spring 17 relative to that of the coil spring 12. When the small pressure of the fluid flowing into the fluid chamber CF is added, the volume of the fluid chamber CF is expanded and the clearance is turned to be D2 as shown in FIG. 15. Then, the fluid is accommodated under the small pressure due to the biasing force of the conned disc spring 17 relative to that of the coil spring 12. A relation between the stroke of the piston 11 and the pressure in the fluid chamber CF of the low-pressure reservoir 10 is as shown in FIG. 27 indicating that a small stroke (Db) of the piston 11 is obtained by the small pressure (Pa) less than the predetermined pressure (Pb) and the fluid with the small pressure (Pa) is accommodated. In the fifth embodiment, since the configuration of the piston 11 is same as that of the above-mentioned embodiments of the low-pressure reservoir and only a space is required for accommodating the conned disc spring 17, the production is simple. The rest configuration of the fifth embodiment of the low-pressure reservoir used in the present invention is substantially same as that of the embodiment in FIGS. 4, 5, so the substantially same parts or components shown in FIGS. 4, 5 bear the same numbers in the fifth embodiment and the explanation is not repeated here.

[0069]FIGS. 16, 17 show the sixth embodiment of the low-pressure reservoir used in the present invention. FIG. 16 shows the condition before the low-pressure reservoir is operated as the capacity means and FIG. 17 shows the condition when the low-pressure reservoir is operated as the capacity means. Also in the sixth embodiment, the elastic member is disposed as the reverse biasing means between the piston 11 and the cylinder 10 a for biasing the piston 11 in the reverse direction to the biasing direction of the coil spring 12. Further, in the sixth embodiment, a coil spring 18 is used as the elastic member. The capacity space of the present invention is configured by an expanded space formed when the volume of the fluid chamber CF is expanded by adjusting the biasing force of the coil spring 18 relative to that of the coil spring 12.

[0070] In the inoperative condition of the capacity means as shown in FIG. 16, a clearance formed between the inner surface of the piston 11 and that of the cylinder 10 a is adjusted to be D3 due to the biasing force of the coil spring 18 relative to that of the coil spring 12. When the small pressure of the fluid flowing into the fluid chamber CF is added, the volume of the fluid chamber CF is expanded and the clearance is turned to be D4 as shown in FIG. 17. Then, the fluid is accommodated under the small pressure due to the biasing force of the coil spring 18 relative to that of the coil spring 12. In the sixth embodiment, in the same way, the relation between the stroke of the piston 11 and the pressure in the fluid chamber CF of the low-pressure reservoir 10 is as shown in FIG. 27 indicating that the fluid with the small pressure (Pa) is accommodated. Further, in the sixth embodiment, the configuration of the piston 11 is same as that of the above-mentioned embodiments of the low-pressure reservoir so that the coil spring 18, which biasing force is easily adjustable as the reverse biasing means, can be used. However, an enlarged diameter portion 1 d is required to be formed in a position facing the piston 11 and being connected to the fluid chamber CF for accommodating the coil spring 18. Since the rest configuration of the sixth embodiment of the low-pressure reservoir used in the present invention is substantially same as that of the embodiment in FIGS. 4, 5, the substantially same parts or components shown in FIGS. 4, 5 bear the same numbers in the sixth embodiment and the explanation is not repeated here.

[0071]FIGS. 18, 19 show the seventh embodiment of the low-pressure reservoir used in the present invention. FIG. 18 shows the condition before the low-pressure reservoir is operated as the capacity means and FIG. 19 shows the condition when the low-pressure reservoir is operated as the capacity means. Also in the seventh embodiment, the elastic member is disposed as the reverse biasing means between the piston 11 and the cylinder 10 a for biasing the piston 11 in the reverse direction to the biasing direction of the coil spring 12. Further, in the sixth embodiment, an elastic resin ring is used as the elastic member. The capacity space of the present invention is configured by an expanded space formed when the volume of the fluid chamber CF is expanded by adjusting the biasing force of the elastic resin ring relative to that of the coil spring 12.

[0072] In the inoperative condition of the capacity means as shown in FIG. 18, a clearance formed between the inner surface of the piston 11 and that of the cylinder 10 a is adjusted to be D5 due to the biasing force of the elastic resin ring 19 relative to that of the coil spring 12. When the small pressure of the fluid flowing into the fluid chamber CF is added, the volume of the fluid chamber CF is expanded and the clearance is turned to be D6 as shown in FIG. 19. Then, the fluid is accommodated under the small pressure due to the biasing force of the elastic resin ring 19 relative to that of the coil spring 12. In the seventh embodiment, in the same way, the relation between the stroke of the piston 11 and the pressure in the fluid chamber CF of the low-pressure reservoir 10 is as shown in FIG. 27 indicating that the fluid with the small pressure (Pa) is accommodated. Further, in the seventh embodiment, since the configuration of the piston 11 is same as that of the above-mentioned embodiments of the low-pressure reservoir and only a space is required for accommodating the elastic resin ring 19, the production is simple. The rest configuration of the seventh embodiment of the low-pressure reservoir used in the present invention is substantially same as that of the embodiment in FIGS. 4, 5, so the substantially same parts or components shown in FIGS. 4, 5 bear the same numbers in the seventh embodiment and the explanation is not repeated here.

[0073]FIGS. 20, 21 show the eighth embodiment of the low-pressure reservoir used in the present invention. FIG. 20 shows the condition before the low-pressure reservoir is operated as the capacity means and FIG. 21 shows the condition when the low-pressure reservoir is operated as the capacity means. In the eighth embodiment, a sub-cylinder 111 connected to the fluid chamber CF is formed at the piston 110. A sub-piston 112 is slidably accommodated in the sub-cylinder 111. Thus, a sub-fluid chamber CS configuring the capacity space of the present invention for accommodating the fluid is formed within the sub-cylinder 111. In addition, as a sub-biasing means, the sub-cylinder 111 accommodates a coil spring 113 therein by which the sub-piston 112 is biased in a direction in which the volume of the sub-fluid chamber CS is reduced.

[0074] In the inoperative condition of the capacity means as shown in FIG. 20, the sub-piston 112 is maintained in an initial position thereof in FIG. 20 by the biasing force of the coil spring 113. Thus, a clearance between the inner surface of the sub-piston 112 and that of the cylinder 10 a is D7. When the fluid flows into the sub-fluid chamber CS, the sub-piston 112 is driven by overcoming the biasing force of the coil spring 113 and then the volume of the sub-fluid chamber CS is expanded. Accordingly, as shown in FIG. 21, the clearance is turned to be D8 where the fluid is accommodated under the small pressure due to the biasing force of the coil spring 113. A relation between a stroke of the sub-piston 112 and the pressure in the fluid chamber CF of the low-pressure reservoir is as shown by the solid line in FIG. 26 indicating that the stroke of the piston 110 cannot be obtained until the pressure in the low-pressure reservoir becomes the predetermined pressure (Pb) or more. However, as shown by the dashed line in FIG. 26, the small stroke (Da) of the sub-piston 112 can be obtained by the small pressure (Pa) less than the predetermined pressure (Pb) so that the fluid with the small pressure (Pa) is, . accommodated in the sub-fluid chamber CS. When the pressure in the fluid chamber CF or the sub-fluid chamber CS is decreased, the sub-piston 112 is returned in the initial position direction thereof by the biasing force of the coil spring 113. Then, the fluid in the sub-fluid chamber CS is returned to the fluid chamber CF.

[0075] In the eighth embodiment, the piston 110 is not configured in the same way as the piston of the above-mentioned embodiments of the low-pressure reservoir though such as the cylinder 10 a is configured in the same way as such as the cylinder of the above-mentioned embodiments of the low-pressure reservoir. However, since the coil spring 113 which biasing force is easily adjusted is used, the specification of the low-pressure reservoir is simply established. Since the rest configuration of the eighth embodiment of the low-pressure reservoir used in the present invention is substantially same as that of the embodiment in FIGS. 4, 5, the substantially same parts or components shown in FIGS. 4, 5 bear the same numbers in the eighth embodiment and the explanation is not repeated here.

[0076]FIGS. 22, 23 show the ninth embodiment of the low-pressure reservoir used in the present invention. FIG. 22 shows the condition before the low-pressure reservoir is operated as the capacity means and FIG. 23 shows the condition when the low-pressure reservoir is operated as the capacity means. In the ninth embodiment, in addition to the embodiment shown in FIGS. 20, 21, a coil spring 114 is provided for biasing the sub-piston 112 in a reverse direction to the biasing force of the coil spring 113. Due to the coil springs 113, 114, the small pressure of the fluid in the sub-fluid chamber CS can be easily adjusted.

[0077] In the inoperative condition of the capacity means shown in FIG. 22 in the ninth embodiment, the sub-piston 112 is maintained in the initial position thereof so that a clearance between the inner surface of the sub-piston 112 and that of the cylinder 10 a is D9. When the fluid flows into the sub-fluid chamber CS, the sub-piston 112 is driven and then the volume of the sub-fluid chamber CS is expanded. Then, as shown in FIG. 23, the clearance is turned to be D10 where the fluid is accommodated under the small pressure due to a balance of the biasing forces between the coil spring 113 and the coil spring 114. Also in the ninth embodiment, as shown by the dashed line in FIG. 26, the small stroke (Da) of the sub-piston 112 can be obtained by the small pressure (Pa) less than the predetermined pressure (Pb) and the fluid with the small pressure (Pa) is accommodated in the sub-fluid chamber CS. Since the rest configuration of the ninth embodiment of the low-pressure reservoir used in the present invention is substantially same as that of the embodiment in FIGS. 20, 21, the substantially same parts or components shown in FIGS. 20, 21 bear the same numbers in the ninth embodiment and the explanation is not repeated here. In the ninth embodiment, the biasing force biasing the sub-piston 112 can be easily adjusted by the coil springs 113, 114 so that the specification of the low-pressure reservoir is established more easily than the embodiment in FIGS. 20, 21.

[0078]FIGS. 24, 25 show the tenth embodiment of the low-pressure reservoir used in the present invention. FIG. 24 shows the condition before the low-pressure reservoir is operated as the capacity means and FIG. 25 shows the condition when the low-pressure reservoir is operated as the capacity means. The sub-cylinder 111 is accommodated in the piston 110 in the embodiment in FIGS. 20, 21, however, the sub-cylinder 111 is accommodated in the housing 1 in the tenth embodiment. In the tenth embodiment shown in FIGS. 24, 25, the sub-cylinder 111 connected to the fluid chamber CF is formed at the housing 1. The sub-piston 112 is slidably accommodated in the sub-cylinder 111. Thus, the sub-fluid chamber CS configuring the capacity space of the present invention is formed in the sub-cylinder 111 for accommodating the fluid.

[0079] As the sub-biasing means, the sub-cylinder 111 accommodates the coil spring 113 therein by which the sub-piston 112 is biased in the direction in which the volume of the sub-fluid chamber CS is reduced. The configuration of such as the piston 11 is substantially same as that of the embodiment in FIGS. 4, 5, so the substantially same parts or components shown in FIGS. 4,5 bear the same numbers in the tenth embodiment and the explanation is not repeated here. Also in the tenth embodiment, as shown by the dashed line in FIG. 26, the small stroke (Da) of the sub-piston 112 can be obtained by the small pressure (Pa) less than the predetermined pressure (Pb) and the fluid with the small pressure (Pa) is accommodated in the sub-fluid chamber CS. In this embodiment, the configuration of the piston 11 is same as that of the above-mentioned embodiments of the low-pressure reservoir and thus the capacity means of the present invention is formed separately at the housing 1. However, the specification of the capacity means is easily established.

[0080] According to each embodiment mentioned above, the excessive fluid in the compression chamber CP flows into the side of the low-pressure reservoir 10 through each discharge permitting means even if the intake valve 7 is in the closed position. The excessive fluid is then accommodated in each capacity means under the small pressure. Thus, the pressure in the compression chamber OP cannot be increased at the next top dead center of the plunger as shown by the solid line in FIG. 31 so that the incidence of the noise can be prevented. With respect to the pressure increase in the compression chamber CP at this moment, the larger the volume ΔQ2 of the fluid flowing into the side of the low-pressure reservoir 10 is than the volume ΔQ1 of the fluid flowing into the compression chamber CP through the discharge 6, the more the pressure in the compression chamber CP is decreased at the next top dead center of the plunger. However, a pump efficiency is decreased if ΔQ2 is excessively large, so ΔQ1 and ΔQ2 are preferably adapted to be approximately equal The plunger pump according to each embodiment mentioned above is suitable for a control device (such as an actuator used for the anti-skid control) in a hydraulic pressure brake device for a vehicle. However, the, present invention is not limited to that particular control device and can reduce the noise at the pump driving when used in various fluid devices.

[0081] The present embodiment of the invention with the forgoing structure has effects hereinafter:

[0082] The plunger pump device of the present invention is provided with the discharge permitting means for permitting the small amount of the fluid to be discharged from the compression chamber into the low-pressure reservoir side even if the intake valve is in the closed position, and the capacity means including the capacity space for accommodating the small amount of the fluid discharged from the discharge permitting means and for accommodating the fluid under the small pressure less than the predetermined pressure. The plunger pump of this invention with the simple structure can easily and surely reduce the noise of the pump device resulting from especially the operation of the discharge valve.

[0083] In the plunger pump device as explained above, since the discharge permitting means can be configured by adding a small modification to the existing device, the noise can be reduced without causing the enlargement of the device.

[0084] Further, In the plunger pump device as explained above, since the capacity means can be simply configured, the noise can be reduced without causing the enlargement of the device.

[0085] The principles, preferred embodiment and mode of. operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the sprit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby. 

What is claimed is:
 1. A plunger pump device comprising: a housing defining a compression chamber; a plunger slidably accommodated in the housing and exposed to the compression chamber at one end; a drive means for reciprocating the plunger; a discharge valve connected to the compression chamber; an intake valve connected to the compression chamber; a low-pressure reservoir for accommodating fluid with a predetermined pressure or more connected to the compression chamber through the intake valve; a discharge permitting means for permitting a small amount of the fluid to be discharged from the compression chamber into the low-pressure reservoir side even if the intake valve is in a closed position; and a capacity means including a capacity space for accommodating the small amount of the fluid discharged from the discharge permitting means and for accommodating the fluid under a small pressure less than the predetermined pressure.
 2. The plunger pump device according to claim 1, wherein the intake valve includes a valve seat and a valve portion always biased to be seated on the valve seat, and a slit is formed on at least either one of the valve portion or the valve seat for configuring the discharge permitting means.
 3. The plunger pump device according to claim 1, wherein the plunger is slidably accommodated in the housing through a seal member for permitting the small amount of the fluid to be discharged from the compression chamber, and the discharge permitting means is configured by the seal member.
 4. The plunger pump device according to claim 1, wherein the low-pressure reservoir includes a cylinder connected to the compression chamber through the intake valve, a piston slidably accommodated in the cylinder and forming a fluid chamber for accommodating the fluid in the cylinder, and a biasing means for biasing the piston in a direction in which the volume of the fluid chamber is reduced.
 5. The plunger pump device according to claim 4, wherein the piston is formed with a concave portion being covered by a diaphragm member on a surface of the piston exposed to the fluid chamber.
 6. The plunger pump device according to claim 5, wherein the capacity space of the capacity means is configured by an expanded space formed in the fluid chamber when.; the diaphragm member is deformed inside the concave portion.
 7. The plunger pump device according to claim 5, wherein the diaphragm member is integrally formed with the piston. 8 The plunger pump device according to claim 4, wherein an annular groove is formed on an outer periphery of the piston and an annular elastic member is inserted into the annular groove for forming a predetermined space therebetween in a sliding direction of the piston.
 9. The plunger pump device according to claim 8, wherein the capacity space of the capacity means is configured by an expanded space formed between the annular elastic member and the annular groove when the annular elastic member is deformed.
 10. The plunger pump device according to claim 4, wherein a reverse biasing means is provided for biasing the piston in a reverse direction to a biasing force of the biasing means.
 11. The plunger pump device according to claim 10, wherein the capacity space of the capacity means is configured by an expanded space in the fluid chamber being expanded by adjusting the biasing force of the reverse biasing means relative to that of the biasing means.
 12. The plunger pump device according to claim 10, wherein the reverse biasing means is an elastic member disposed between the piston and the cylinder.
 13. A plunger pump device according to claim 1, wherein the capacity means includes a sub-cylinder formed at the piston for communicating to the fluid chamber, a sub-piston slidably accommodated in the sub-cylinder and forming a sub-fluid chamber for accommodating the fluid in the sub-cylinder, and a sub-biasing means for biasing the sub-piston in a direction in which the volume of the sub-fluid chamber is reduced.
 14. The plunger pump device according to claim 1, wherein the capacity means includes a sub-cylinder formed at the housing for communicating to the fluid chamber, a sub-piston slidably accommodated in the sub-cylinder and forming a sub-fluid chamber for accommodating the fluid in the sub-cylinder, and a sub-biasing means for biasing the sub-piston in the direction in which the volume of the sub-fluid chamber is reduced.
 15. The plunger pump device according to claim 3, wherein the seal member is provided between a first annular groove and the compression chamber and inserted into a second annular groove so as to form a small space therebetween for permitting the small amount of the fluid to be discharged from the compression chamber.
 16. The plunger pump device according to claim 15, wherein a hydraulic passage is formed between the seal member and the second annular groove for permitting the small amount of the fluid to be discharged from the compression chamber under a compressed condition thereof.
 17. The plunger pump device according to claim 15, wherein a seal member is provided between the drive cam and the first annular groove. 